1. Field of the Invention
The present invention relates to an oscillating piston flowmeter including a measuring chamber having a bottom, a cylindrical jacket, a central journal, a guide ring, a separating wall, and inlet and outlet openings; and a piston located in the measuring chamber and having a bottom, a cylindrical skirt, a pilot journal engageable with and rotatable about the central journal of the measuring chamber, and a guiding slot extending in the skirt and the bottom and up to separating wall of the measuring chamber.
2. Description of the Prior Art
Oscillating piston flowmeters, which relate to volumetric flowmeters, include a measuring chamber through which an entire amount of a liquid flows. At that, a portion of the potential energy of the to-be-measured water, which energy is used for driving the flowmeter, becomes lost. The resulting pressure drop is indicated as pressure loss P. The pressure drop is caused by a change of direction of water flow, a change of a cross-section of the water conduit along the path of water flow, etc.
There is arranged in the measuring chamber an oscillating piston which is displaced during the measuring process from a high pressure side to the low pressure side. This takes place automatically under the action of the water flow which regularly splits in the measuring chamber in a plurality of streams. Upon rotation of the piston, two different volumes of constant predetermined magnitudes are conveyed. At that, the lower pilot journal of the piston rotates about the central journal of the measuring chamber.
The piston skirt has a slot along its entire height. Upon rotation of the piston, this slot reciprocates along the separating wall which is provided in the measuring chamber. The advantage of the reciprocating movement consists in that the piston automatically returns in its initial position without any need in additional control devices, valves, slides, etc. Inner and outer piston guide means insure the necessary movement of the piston. The piston is also provided with an upper journal which drives a driver which transmits the circular movement of the upper journal to a counter.
The measurement precision of oscillating piston flowmeter to a large extent depends on the dimensional accuracy of the elements of the measuring chamber. The smaller is the clearance between the piston and the measuring chamber the less amount of liquid can pass unnoticed, and the smaller is the measurement error. However, from a functional point of view, a minimal clearance between the piston and the measuring chamber is needed to prevent the piston from jamming. A typical magnitude of the clearance between movable parts is smaller of or equal to 10 .mu.m. Often, the to-be-measured liquid contains dirt particles, e.g., rust, sand and the like, in case of drinking water. Often different salts precipitate from a liquid, e.g., lime in case of the drinking water. As a rule, these foreign substances pass past the piston without problems. However, now and then it may occur that these particles accumulate in the functional clearance between the piston and the wall of the measuring chamber.
When these particles are loose, they are pushed by the piston to the measuring chamber, without causing any trouble. At that, the movement of the piston slightly slows down, without noticeably affecting the measurement accuracy.
However, when the particles stuck in the clearance, they can block the movement of the piston, and the flowmeter fails.
Further, there exists a possibility of the piston being rubbed by the particles. This may result in formation of scratches in the walls of the piston and/or the measuring chamber, which increase the actual clearance between the piston and the wall of the measuring chamber. This does not result in a failure of the flow-meter, but its measurement accuracy is reduced.
Accordingly an object of the present invention is to provide an oscillating piston of the above-described type in which the blocking of the piston movement is prevented and a possibility of a damage the walls of the piston and the measuring chamber is substantially reduced.